The present invention relates to a microencapsulated cockroach-controlling composition wherein an insecticide having a 3-phenoxybenzyl group and phenylxylylethane are encapsulated in microcapsules having polyurethane wall which have an average particle diameter of not more than 80 .mu.m, a wall thickness of not more than 0.3 .mu.m and a value of the average particle diameter/wall thickness of 100-400.
Controlling cockroach has been mainly carried out by a residual spray method.
At present, formulations such as emulsifiable concentrate, solubilized emulsion concentrate and oil solution which contain, for example, an organophosphorus insecticide or pyrethroidal insecticide as an active ingredient are used for the residual spray.
Especially residual efficacy and safety are desired factors to formulations used for the residual spray. If the residual efficacy is to be enhanced with the conventional formulations such as emulsifiable concentrate, solubilized emulsion concentrate and oil solution a high application dosage is required, which may bring about problem in safety. Thus, formulations being safer and having greater in efficacy are increasingly demanded.
Under the circumstances, research and development of so-called microencapsulation technique that an active ingredient is enclosed in a wall material have become intensive. As microencapsulated insecticides, those which contain organophosphorus insecticide as an active ingredient are disclosed in Japanese Patent Kokai No. 62-161706 and those which contain pyrethroidal insecticide as an active ingredient are disclosed in Japanese Patent Kokoku No. 55-38325.
In some cases, microencapsulation of insecticides might be effective for improving residual efficacy.
However, residual efficacy of microencapsulated insecticides varies depending upon a particle diameter of microcapsule and a wall thickness. Optimum particle diameter and wall thickness should be chosen in order to maintain residual efficacy for a prolonged period of time. The optimum range naturally varies depending on varieties of insect pests to be controlled and of insecticides.
In general, microencapsulation of insecticides having a polyurethane wall is performed by interfacial polymerization using a polyfunctional isocyanate.
The interfacial polymerization method essentially requires a step of homogeneously mixing an active ingredient to be enclosed in capsules with polyfunctional isocyanate.
In the case when the active ingredient is a pyrethroidal insecticide, an organic solvent may be added as so-called cosolvent when the insecticide is mixed with a polyfunctional isocyanate which is sometimes high in viscosity, since this insecticide is generally high in viscosity and sometimes is in the form of crystal. Japanese Patent Kokoku No. 55-38325 mentions "For example, as usual organic solvents, there may be selected from hydrocarbons such as xylene, toluene, hexane and heptane, chlorinated hydrocarbons such as carbon tetrachloride and chloroform, ketones such as methylisobutyl ketone, methyl ethyl ketone and cyclohexanone and esters such as diethyl phthalate and n-butyl acetate."
However, these known techniques are not necessarily satisfactory when some pyrethroidal insecticides are used as an active ingredient for cockroach-controlling.
The inventors have made intensive study on optimum ranges of particle diameter and wall thickness of microcapsules and on selection of optimum organic solvents when an insecticide having a 3-phenoxybenzyl group is encapsulated as a core material in a polyurethane wall and then this is used for cockroach-controlling.
As a result, it has been found that some insecticides having a 3-phenoxybenzyl group microencapsulated as a core material in polyurethane wall using phenylxylylethane as a cosolvent have residual efficacy for a prolonged period of time for cockroach-controlling.